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HOWMEDIUM VOLTAGE METALCLAD SWITCHGEAR HAS EVOLVED (VD4 & UNIGEAR)
INDOOR AIR INSULATED SWITCHGEARVacuum Solution
UniGear ZS1 with VD4/Vmax upto 12KV application UniGear ZS2 with VD4 36 for 36KV application
UNIGEAR PANEL TYPE
Single Busbar standard depthdeeper versionFloor rolling versionDouble Busbar versionUnigear ZS2 for 36KV
UNIGEAR SINGLE BUSBAR
Rated Voltage (kV)121212Dry Power frequency High Voltage (kV)282828Impulse withstand Voltage(kVpk)757575 Rated Frequency (Hz)505050 Rated Current of Main Busbar (A)630 to 12501250 to 20002500 to 3150/4000 Rated Short- Time withstand current (kA)26.3/3 sec26.3/44/3 sec44/3sec Peak withstand Current (kApk)6666/110110 Rated current of circuit breaker (A)630 to 1250630 to 20002500 to 3150
UNIGEARZS1- DOUBLE BUSBARZS2 Rated Voltage1236Impulse withstand Voltage(kVpk)75/9575/95 Rated Frequency (Hz)5050 Rated Current of Main Busbar (A)1250 to 31502000/2500 Rated Short- Time withstand current (kA)44/3Sec31.5/3Sec
Peak withstand Current (kApk)6654
Rated current of circuit breaker (A)1250 to 31502000/2500
UNIGEAR PANEL COMPONENTSLow Voltage CompartmentGas exhaust ductBusbar Compartment Feeder Compartment Circuit breakerCircuit breaker Compartment Withdrawable voltage transformer with fuses
UNIGEAR FEATURESUse of Alu-Zinc coating instead of conventional paint, making it more environmental friendly.Internal arc proof with 1Sec. Test durationSelf supported, Busbar design without conventional support insulator.Specialized design/construction of cubicles CBs, Busbar, PTs
PANEL INTERNAL INTERLOCKINGCircuit breaker can only be moved from the test position when both the CB and Earthing switch are off.CB can only be switched ON when breaker is in the test or service position.CB rack IN/OUT is possible only when there is supply to control plug.Earth switch can be closed only if the circuit breaker is in test position.Connecting & Disconnecting of the control plug is only possible in the CB test position.If the Earthing switch is ON, the CB cannot be moved from the test to service position.
THE ADVANTAGES BROUGHT BY UNIGEARIt is aimed at making AIS more compact and better customization over a varied range of voltage & current.It uses tubular bus bars which requires less phase clearance compared to rectangular bus bars.It has reduced the use of insulators thereby greatly reducing the chance of insulator tracking.It is also emphasizing on the use of voltage detecting insulators which can act as a direct replacement of PT.It has an improved external earthing truck, with more refined interlock.
BRIEF HISTORY OF VACUUM CIRCUIT BREAKER Vacuum switching technology was developed originally in the USA in the 1920s but remained non-viable until the late 1940s and early 1950s.English Electric created an almost perfect material with the invention of CLR Chrome copper contact material, patented in 1970.Slowly came the improvement in the interrupter construction, its manufacturing and arc control technique. The market for vacuum circuit breakers finally came to prominence from early 1970s
ARC QUENCHING INSIDE VACUUM INTERRUPTERAt the instant of de-touching of contacts in a vacuum, the increased current density make the metal on the contact surface easily vaporize and create a conducting media for arc path. The arc gets initiated and continues until the next current zero.At current zero the arc is extinguished and the conducting metal vapour is re-condensed on the contact surface. At this point, the transient recovery voltage that develops cannot create the electron avalanche necessary to attain the breakdown voltage of the vacuum. Thus, the arc cannot be re established again after current zero.
VD4 VACUUM CIRCUIT BREAKER
A LOOK AT THE PROS AND CONS OF VACUUM SWITCHING Vacuum switching has the most effective arc quenching ability and a low life cycle cost upto 52 KV.It is more environment friendly and practically maintenance free. It is effective in tackling the problem of current chopping. VCB uses Butt type contact with CuCr as the contact material because of its good electrical and mechanical properties. CuCr is also resistant to solid welding that may otherwise occur at load closing or short circuit conditions.
Vacuum medium has an effective dielectric ceiling of 500 KV which roughly corresponds to LIWL of 132 kV voltage medium. Beyond 132 KV chances of X-Rays emission from the vacuum interrupters cannot be ruled out.High contact pressure upto 600 daN for fault level of 50 KA may be required to prevent popping. It is to monitor the condition of the vacuum. A pressure of 10^-4 to 10^-8 mbar must be maintained.
VD4 INTERRUPTERIn the circuit-breaker of type VD4,
the complete pole and the maintenance freevacuum interrupter form a positive unit.This is achieved by a specially developed casting technique in which the vacuum interrupter is
directly embedded in epoxy resin to form a complete pole.Disruptive external effects on the switching element are therefore
extensively precluded.For very high rated currents, rated short-circuit breaking currents and for rated voltages upto 36 kV, they are usedThe contact gap of only 12 mm is sufficient to provide high dielectric strength.
Arc Control techniqueThere can be two types of arc that can develop inside a vacuum Interrupter the Diffused arc and the Constricted arc.The diffused arc is a natural outcome for fault current upto 10 KA whereas constricted arc appears above 10 KA fault current.In diffused arcing the arcs are uniformly distributed over the entire contact surface whereas in constricted arcing the arc tends to localize on a certain spot causing damage to the interrupter contacts.The objective of arc control technique is to prevent formation of constricted arcing and keep diffused arcing irrespective of the fault current vale.This is achieved by developing either a Radial Magnetic Field or Axial Magnetic Field around the arc using the arc current.VD4 uses Radial Magnetic Field as arc control technique.
VD4 KEY ASPECTS AND STRENGTHSApplication where space saving is a premium The panel contacts are mounted in the bushing and the metallic shutters are provided hence, better compartmentalization is achieved.
Higher reliability and availability and longer life with fewer fastening parts.It has moulded case design protecting the vacuum interrupters from impact, dust, and condensation. High dielectric protection of the vacuum interrupters without additional modifications.VD4 with manual mechanism is suitable for auto reclosing.It has only one type of operating mechanism (EL) for all the VD4 variants.
FIELD OF APPLICATIONSVacuum circuit-breaker of type VD4 is designed for switching:Power Transmission and distribution substationsMotor control and protection Capacitor bank control and protection Transformers and Generators under load and no-load conditionsCables and overhead lines under load and no-load conditions
FEATURES & OVERVIEWVacuum interruption techniqueContacts in vacuum protected against oxidation and contamination Sealed for life vacuum interrupters In accordance with IEC 62271-100 STDs Operation sequence O - 0.3 - CO - 15 - COLimited switching energy10,000 mechanical operationsStored energy operating mechanism with built-in anti-pumping device and closing spring charging lever Insulating monoblocOperating mechanism and monobloc fixed to a sturdy metal frameEasy customization with a complete range of accessoriesLocks to prevent incorrect and hazardous operations
VD4 - OVERVIEWOpen/close aux. contacts (standard set of ten aux.c.)Additional opening releaseLocking magnet in the actuatorOpening pushbuttonClosing pushbuttonShunt tripping releaseBuilt-in lever for closing spring manual charging Undervoltage release (missing in the picture)Shunt closing releaseSignaling device for closing springs charged/dischargedMechanical operation counterGeared motor for closing spring charging
VD4 - STANDARD EQUIPMENTMechanical signalling device for CB open/closedMechanical signalling device for closing spring charged/dischargedOpening and closing pushbuttonsMechanical operation counterBuilt-in lever for manually charging of closing springAnti-pumping mechanical built-in function5 + 5 auxiliary contactsConnection terminals and terminal board for auxiliary circuits (for fixed CB)Isolating contacts, cord with connector (plug only), racking-in/out lever (for withdrawable CB)
Brief view of Interrupter structureThe Vacuum Interrupter is housed inside a ceramic porcelain cylinder having Alumina 94% and Silica 6%.The Shield is made of oxygen free Copper and is primarily used to capture the metal vapour produced during arcing thereby maintaining the internal insulation of the ceramic porcelain cylinder.The shield also prevents direct exposure from the high fault current/arc.The bellows allow the motion of the movable contact while maintaining vacuum tight seal where the speed of the movable contact reaches from 0 to 2 m/s in less than 100 micro second.The impulse motion parted to the bellows are non uniform and anti twist bushings are provided to improve the mechanical strength of the bellows.
Vacuum Circvuit Breaker type VD-4Rated VoltageKV1217.53640.5Rated CurrentA1250 - 25003150 - 40001250-25003150-40001250-31501250-3150Rated Short Circuit Symmetrical current breaking capacityKA40505320-50634020-4025-4025-31.5Rated Short Circuit Asymmetrical current breaking capacityKA43.656.866.521.7-56.865.643.621.7-43.621.7-43.627.3-34.3Rated Short Circuit Making current capacityKA10012515830-12515810050-1006